The causes of alopecia are considered to be related to disturbances in hormone balance, disturbances of circulation of capillaries surrounding hair papillae and hair follicles, excessive hyperfunction of sebaceous glands or deficient sebum secretion, accumulation of stress, declines in immune function, hypofunction in hair matrix cells, abnormal activity of various enzymes involved in hair growth, excessive dandruff formation (abnormal sebum secretion/proliferation of scalp bacteria), scalp tension, excessive dryness, and the like.
In order to prevent such hair loss, stimulate hair growth, and promote hair growth (new hair growth), the following measures are believed to be effective:
(1) promotion of local blood circulation and metabolism
(2) promotion of proliferation of hair follicle cells
(3) Prevention of hair loss caused by androgens and suppression of sebum secretion
(4) Preservation of scalp environment
Healthy human hair is shed and replaced by new growth at a cycle of about 5 or 6 years.
This cycle is classified into three phases: an “anagen” in which the hair follicle is formed and hair grows, a “catagen” in which growth regresses, and a “telogen” in which growth stops.
In male-pattern hair loss, it has been known that the hair cycle gradually shortens, the anagen phase becomes shortened, and as a result, thick, long terminal hair transforms into lanugo-like vellus hair.
By promoting blood flow in the scalp, oxygen and nutrients are supplied to hair follicles via capillaries mainly in hair papillae and in the periphery of mesenchymal cells surrounding hair follicles, and then cause epithelial cells, such as hair matrix cells, to proliferate smoothly, which is thus believed to be effective, in particular, in the anagen phase. However, a detailed mechanism thereof has not been clarified.
In addition to blood circulation promotion, vasodilation, and energy supply, many studies have been conducted on drugs for balancing hormones, which have hair loss suppression and hair growth promotion effects from the standpoint of androgen suppression.
Although the hair loss mechanism has not been sufficiently elucidated, the development of hair restoring drugs is in progress from this viewpoint.
Additionally, although not yet in the drug development stage, studies have been conducted as to the effects of cell growth factors and substances, such as neurotransmitters, on cells constituting hair follicles, as to association of apoptosis-related substances, hair follicle-inducing factors, angiogenesis factors, and the like with the hair cycle, as to hair growth promotion thereof, prolongation of the anagen phase, and the like.
It has been reported that, even in male-pattern hair loss, a slight inflammation is caused around hair follicles although not so severe as that seen in alopecia areata. Studies are being conducted on cytokines in association with male-pattern hair loss.
Fewer studies have been conducted on thinning hair in women than on thinning hair in men.
However, in recent years, the number of women worrying about thinning hair has been increasing.
This is said to be caused by stress resulting from women's social advancement and the like.
In male-pattern hair loss, it is known that since the hair follicle growth phase shortens, the number of immature hair follicles increases, resulting in an increase in lanugo-like hair.
On the other hand, in women, since the anagen ratio does not substantially change, the reason for thinning hair is believed to be transformation of terminal hair into fine hair, rather than an increase of lanugo-like hair.
That is, it is believed to be possible to grow thick hair by thickening hair follicles and moreover by actively proliferating hair follicle cells.
It is known that, the hair root of anagen hair is embedded deep into the fatty layer under the dermis, and when the anagen phase lasting about 5 to 6 years ends, the hair root gradually shortens to about a half through the catagen phase to the telogen phase.
When a new anagen phase is initiated, the hair root is gradually embedded deep into the fatty layer again, and new hair growth starts.
It has been confirmed that, during the time when the anagen hair follicle grows, many positive cells are observed in hair matrix cells around the hair papilla and root sheath cells around the hair shaft.
Consequently, under the assumption that it is important for improving women's thinning hair to promote proliferation of root sheath cells, research has been conducted on the development of drugs for promoting cell proliferation in cell culture systems.
On the other hand, for example, as seen in Japanese Unexamined Patent Application Publication No. 4-5219 (Patent document 1) and Japanese Unexamined Patent Application Publication No, 5-25023 (Patent document 2), research has been conducted on hair growth and hair restoration components containing a steroid glycoside and/or a triterpenoid glycoside.
Furthermore, for example, Japanese Unexamined Patent Application Publication No. 7-109295 (Patent document 3) discloses a hair growth and hair restoration material containing, as an active ingredient, a stigmasterol glycoside which is a type of steroid glycoside.